SOME years ago Willhalm et al. ' reported the mass spectra of a number of chromanes, unsubstituted in the heterocyclic ring. In the mass spectrum of chromane itself (C6H4(CH2),0, M = 134) they observed two diffuse peaks, which were proposed to account for the formation of the [M -15]+-ion, viz. at m* = 105-5, corresponding with the transition m/e 134 (parent) + m/e 119, and at m* = 106.5, corresponding with the transition m/e 133 (parent-1) -+ m/e 119. The last reaction would be very interesting, because it involves the expulsion of a methylene group, a rare process in mass spectrometry.2 Recently Djerassi's group3s4 has tried to elucidate the pathway for formation of the [M -15]+-ion during cleavage of chromane by use of specifically deuterated analogues. This investigation showed that exclusively hydrogen atoms of the heterocyclic ring participate in a random fashion in the loss of a methyl group from the molecular ion of chromane. The diffuse peak at m* = 106.5 was not observed, however. Therefore the expulsion of methylene from the [M -l]+-ion was excluded.
In a private discussion on this problem with Dr A. F. Thomas' it was decided to reinvestigate this problem. The following results were obtained :